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UNITED STATES DEPARTMENT OF AGRICULTURE 




BULLETIN No. 404 

Contribution from the Bureau of Plant Industry 
WM. A. TAYLOR, Chief 




Washington, D. C. 



PROFESSIONAL PAPER 



October 14, 1916 



HEMP HURDS AS PAPER-MAKING MATERIAL. 

By Lyoter H. Dewby, Botanist in Charge of Fiber-Plant Investigations, and Jason L. 
Merrill, Paper-Plant Chemist, Paper-Plant Investigations. 



CONTENTS. 



The production and handling of hemp hards, 

by Lyster H. Dewey: 

What hemp hards are 

Pith, wood, and fiber 

Character of hurds affected by retting 

Proportion of hurds to fiber and yield per 

acre 

Hurds available from machine-broken 

hemp.... 

Present uses of hemp hurds 

Pre s en t supplies of hurds available 

Baling for shipment 

Cost of baling 

Summary 



Page. 



Page. 
The manufacture of paper from hemp hurds, 

by Jason L. Merrill: 

Introduction 7 

Factors justifying an investigation of hemp 

hurds 

Character of the material 

Character of the tests 

Operations involved in a test 

Description of tests 

Comparison of the tests and commercial 

practice 

Physical tests of the papers produced 24 

Conclusions 25 



In preparing the report on the manufacture of paper from hemp 
hurds it became evident that a short discussion of the agricultural 
aspects of this material should be included in the publication. Such 
an article was prepared, therefore, and the two reports are here pre- 
sented together. 



THE PRODUCTION AND HANDLING OF HEMP HURDS. 

By Lyatbr H. Dewby, Botanist in Charge of Fiber-Plant Investigations. 
WHAT HEMP HURDS ARE. 

The woody inner portion of the hemp stalk, broken into pieces and 
separated from the fiber in the processes of breaking and scutching, 
is called hemp hurds. These hurds correspond to shives in flax, but 
are much coarser and are usually softer in texture. 

Not*.— This bulletin should be useful to all persons who are interested in the economic phases of paper 
making, especially to print and book paper manufacturers. It also should be of interest to scientific inves- 
tigators and chemists. 

61 W-BulL 404—16—1 



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2 BULLETIN 404, U. S. DEPARTMENT OP AGRICULTURE. 

The hemp stalk grown in a broadcast crop for fiber production is 
from one-eighth to three-eighths of an inch in diameter and from 4 to 
10 feet tall. The stalk is hollow, with a cylindrical woody shell, thick 
near the base, where the stalk is nearly solid, and thinner above, where 
the hollow is relatively wider. 

In the process of breaking, the woody cylinder inside of the fiber- 
bearing bark is broken into pieces one-half of an inch to 3 inches long 
and usually split into numerous segments. The thicker lower sec- 
tions are split less than the thin-shelled upper ones, and they are often 
left quite solid. 

PITH, WOOD, AND FIBER. 

The inner surface of the hurds usually bears a layer of pith, consisting 
of thin-walled cells nearly spherical or angular, but not elongated. 
They are more or less crushed and torn. They are probably of little 
value for paper, but they constitute less than 1 per cent of the weight 
of the hurds. The principal weight and bulk consist of slender elon- 
gated woody cells. The outer surface is covered with fine secondary 
fibers composed of slender elongated cells, tougher than those of the 
wood but finer and shorter than those of the hemp fiber of commerce. 
No method has been devised thus far which completely separates 
from the hurds all of the long fiber. From 5 to 15 per cent of the 
weight of the hurds consists of hemp fiber, in strands from 3 inches 
to 8 feet in length. Some fragments of the bark, made up of short 
cubical cells, usually dark in color, cling to the strands of fiber. 

CHARACTER OF HURDS AFFECTED BT RETTING. 

Nearly all of the hemp in the United States is dew retted. The 
stalks are spread on the ground in swaths, as grain is laid by the cradle. 
The action of the weather, dew, and rain, aided by bacteria, dissolves 
and washes out the green coloring matter (chlorophyll) and most of 
the gums, leaving only the fibrous bark and the wood. The plants in 
this process lose about 60 per cent of their green weight, or about 40 
per cent of their air-dry weight. 

The stalks are sometimes set up in shocks to cure before retting, 
and after retting they are set up in shocks to dry. Each time the 
stalks are handled they are chucked down on the ground to keep the 
butts even. In these operations sand and clay are often driven up 
into the hollow at the base of the stalks, and this dirt, which often 
clings tenaciously, may constitute an objectionable feature in the use 
of hemp hurds for paper stock. 

In Italy and in most localities in Russia and Austria-Hungary 
where hemp is extensively cultivated, it is retted in water, but water 
retting has never been practiced in the United States except to a 
limited extent before the middle of the last century. Hurds from 



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HEMP HURDS AS PAPER-MAKING MATERIAL. 8 

water-retted hemp are cleaner and softer than those from dew-retted 
hemp. 

The fiber is sometimes broken from dry hemp stalks without retting. 
The birds thus produced contain a small percentage of soluble gums, 
chiefly of the pectose series. Comparatively little hemp is prepared 
in this manner in America. 

Process retting by means of weak solutions of chemicals or oils in 
hot water is practiced to a limited extent. The hurds from these 
processes may contain traces of the chemicals or oils and also soluble 
gams in greater degree than those of the dew-retted or water-retted 
hemp. 

PROPORTION OF HURDS TO FIBER AND YIELD PER ACRE. 

The yield of hemp fiber varies from 400 to 2,500 pounds per acre, 
averaging 1,000 pounds under favorable conditions. The weight of 



fta. L— Hemp-breaking machine. The stalks are fed sidewiae in a continuous layer 2 to 3 inches thick, 
turning oat about 4,000 pounds of clean fiber per day and five times as much hurds. 

hurds is about five times that of the fiber, or somewhat greater from 
hemp grown on peaty soils. A yield of 2 J tons of hurds per acre may 
be taken as a fair average. 

HURDS AVAILABLE FROM MACHINE-BROKEN HEMP. 

Hemp hurds are available only from hemp which is broken by 
machines, when the hurds may be collected in quantity in one place 
(figs. 1 and 2). Most of the hemp in Kentucky is still broken by 
hand brakes. These small brakes are moved from shock to shock, so 
that the hurds are scattered all over the field in small piles of less 
than 50 pounds each, and it is the common practice to set fire to them 
is soon as the brake is moved. It would be difficult to collect them 
tt a cost which would permit their use for paper stock. 

Where machine brakes are used, the hemp stalks are brought to the 
machine as grain is brought to a thrashing machine, and the hurds 



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4 BULLETIN 404, U. S. DEPAETMENT OP AGRICULTURE. 

accumulate in large piles, being blown from the machine by wind 
stackers. 

Machine brakes are used in Wisconsin, Indiana, Ohio, and Califor- 
nia, but to only a limited extent in Kentucky. Five different kinds 
of machine brakes are now in actual use in this country,' and still 
others are used in Europe. All of the best hemp in Italy, command- 
ing the highest market price paid for any hemp, is broken by machines. 
The better machine brakes now in use in this country prepare the 
fiber better and much more rapidly than the hand brakes, and they 
will undoubtedly be used in all localities where hemp raising is intro- 
duced as a new industry. They may also be used in Kentucky when 
their cost is reduced to more reasonable rates, so that they may 
compete with the hand brake. Hemp-breaking machines are being 



Fig. 2.— Machine brake and hemp hards. Hemp hurds from machine brakes quickly a/wiwuii^ia tn 

large piles. 

improved and their use is increasing. The hemp-growing industry 
can increase in this country only as machine brakes are developed to 
prepare the fiber. A profitable use for the hurds will add an incentive 
to the use of the machine brake. 

PRESENT USES OF HEMP HURDS. 

Hemp hurds are used to a limited extent for barnyard litter and 
stable bedding, as a substitute for sawdust in packing ice, and, in 
rare instances, for fuel. They are not regarded as having a commer- 
cial value for any of these uses, though they are doubtless worth at 
least $1 per ton on the farm when used for stable bedding. They are 
a waste product, without value for other purposes which might com- 
pete with their use for paper stock. 



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HEMP HT7RDS AS PAPER-MAKING MATERIAL. 5 

PRESENT SUPPLIES OF HURDS AVAILABLE. 

During the last season, 1915, about 1,500 acres of hemp have been 
harvested outside of Kentucky and in regions where machine brakes 
are used. Estimating the yield of hurds at 2£ tons per acre, this 
should give a total quantity of about 3,750 tons. Large quantities of 
hemp from the crop of 1914, which are still unbroken in these areas, 
and large piles of hurds undisturbed where the machines have been 
used during the last two or three years, increase the total to more 
than 7,000 tons. Hemp is now grown outside of Kentucky in the 
vicinity of McGuffey, east of Lima, Ohio; around Nappanee, Elkhart 
County, and near Pierceton, in Kosciusko County, Ind.; about Wau- 
pun and Brandon, Wis.; and at Rio Vista and Stockton, Cal. 

In Kentucky, hemp is grown in most of the counties within a radius 

of 50 miles of Lexington. No accurate statistics of the acreage are 

collected, but the crop harvested in 1915 is estimated at 7,000 acres. 

A machine brake will probably be used in Bourbon County and also 

in Clark County, but most of the hemp in Kentucky will be broken on 

hand brakes. 

BALING FOR SHIPMENT. 

The hurds will have to be baled to facilitate handling in transpor- 
tation and to economize storage space at the paper mills. The bales 
will need to be covered with burlap or some material to keep them 
from shaking out. They may be baled in the same presses that are 
used for baling hemp fiber, but care must be exercised to avoid break- 
ing the press, for the hurds are more resistant than hemp fiber. A 
bale of hemp 2 by 3 by 4 feet weighs about 500 pounds. A bale of 
hurds of the same size will weigh about one-third less, or approxi- 
mately six bales per ton. 

Rough hemp fiber as it is shipped from the farm is not covered; 
therefore, the covering material must be purchased especially for the 
hurds. A piece of burlap about 36 by 48 inches placed on either side 
of the bale will be sufficient, but these pieces, weighing about 3 
pounds each, cost about 40 cents a pair. Baling rope, in addition to 
jute covering, will cost at least 5 cents per bale, making the total cost 
of covering and ties $2.70 or more per ton. Possibly chip board, 
costing about $33 per ton, or not more than 5 cents for the two pieces 
for each bale, may be used in place of burlap. Chip board, burlap, 
and also rope ties may all be used for paper stock. Burlap covers 
might be returned, to be used repeatedly until worn out, but chip 
board could not be used more than once. 

COST OP BALING. 

If burlap covers are used the cost of baling, including covering, ties, 
use of baling press, power, and labor will amount to at least 60 cents 
per bale, or about $3.75 per ton. If chip board can be used the cost 



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6 BULLETIN 404, U. S. DEPABTMENT OP AGRICULTUBE. 

may be reduced to about $2 per ton. The cost of hauling and loading 
on the cars will vary from SI to $3 per ton, depending upon the dis- 
tance and the roads. The farmer must therefore receive from $4 to 
$6 per ton for the hurds, baled, on board cars at his home station. 

SUMMARY. 

Hemp hurds are the woody inner portion of the hemp stalk, broken 
into pieces in removing the fiber. 

They are not used at present for any purpose that would compete 
with their use for paper. 

Hurds are available only from machine-broken hemp, for the cost 
of collecting them from the hand brakes would be too great. 

About 7,000 tons are now available in restricted localities in Ohio, 
Indiana, Wisconsin, and California. 

The quantity is likely to increase as the use of machine brakes 
increases. 

The hurds may be baled in hemp-fiber presses, with partial burlap 
covers like those on cotton bales, or possibly chip-board covers. 

It is estimated that the farmers may deliver the bales on board 
cars profitably at $4 to $6 per ton. 



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THE MANUFACTURE OF PAPER FROM HEMP HURDS. 

By Jason L. Merrill, Paper-Plant Chemist, Paper-Plant Investigations. 
INTRODUCTION. 

The purpose of this paper is to report upon preliminary tests which 
were conducted to determine the paper-making value of hemp hurds, 
a crop waste of the hemp-fiber industry. 

The search for plant materials capable of being utilized in paper * 
nfcnuf acture is a comparatively recent but world-wide activity which 
has for its object the husbanding of present sources of paper-stock 
supply by the substitution of new materials for some of those which 
are rapidly becoming less plentiful and more costly. 

The abstract idea of utilizing that which is at present a waste can 
play no important rdle in such activities, the successful commercial 
outcome of which must be based on the three fundamental factors — 
market or demand for product, satisfactory raw material, and cost. 

Since hemp hurds are to be treated in this report as a raw material 
for the manufacture of book and printing papers, the qualities, supply, 
probable future, and cost of the material will be considered in com- 
parison with wood, with which it must compete. There seems to be 
little doubt that the present wood supply can not withstand in- 
definitely the demands placed upon it, and with increased scarcity 
economy in the use of wood will become imperative. This effect is 
already apparent in many wood-using industries, and although the 
paper industry consumes only about 3 per cent of the total forest cut, 
it is probable that it will be affected through this economy. Our 
forests are being cut three times as fast as they grow, and as wood 
becomes more expensive proper growing and reforesting will receive 
more attention. Thus, naturally, a balance will be established be- 
tween production and consumption, but as this condition approaches 
its limiting values the price of wood may rise to such levels that there 
will be a demand for other raw materials. 

The use of waste paper in conjunction with chemical wood pulp 
has increased to enormous proportions, and it is probable that the 
increase will continue. Although it is a cheaper raw material than 
wood, it is reasonable to suppose that as the wood supply decreases 
and the price of wood pulp advances, the price of waste paper will 
advance somewhat proportionately. 

In view of these conditions it is advisable to investigate the paper- 
making value of the more promising plant materials before a critical 
51647°— Bull. 404—16 2 7 



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8 BULLETIN 404, U. S. DEPARTMENT OF AGRICULTURE, 

situation arises. To be of substantial value the investigations should 
include not only a determination of the quality and quantity of pulp 
and paper which the material is capable of producing, but should 
embrace a consideration of such relevant factors as agricultural con- 
ditions, farm practice, assembling conditions, transportation, and 
probable future supply. 

Certain cultivated plants seem particularly promising, because in 
the harvesting of the regular crop that portion which might be utilized 
for paper manufacture necessarily is either wholly or partially as- 
sembled. To this class of plants belong corn, broom corn, sorghum, 
sugar cane, bagasse, flax, hemp, and the cereal straws. 1 

It is generally conceded that the employment of different raw 
materials would probably yield products of a somewhat different 
quality than those now prevailing in the markets, but the qualities of 
papers and the public demands are so diversified and numerous that 
this possible objection should not be serious. Ten years ago sul- 
phite manufacturers would not accept consignments of spruce Jogs 
if they contained over 5 per cent of fir, while to-day many manufac- 
turers tolerate 50 per cent. Rope papers are found to contain not 
only jute, but when this raw material is not plentiful, chemical pulp 
of various kinds. " Linen paper" is often no more than a trade term. 
Not long ago printing papers were made entirely from chemical wood 
pulp, but to-day if it is desired to secure paper which is free from 
ground wood the specifications must so stipulate. Writing papers, 
formerly made entirely from rags, now are likely to contain either 
chemical or even ground-wood pulp unless the specifications prohibit 
it. Without doubt, many paper manufacturers have maintained cer- 
tain papers up to a fixed standard for a long series of years, but it 
is equally true that competition has lowered the standard of a great 
many papers, some of which had acquired a distinctive recognition. 
The employment of plant fibers will not necessarily lower the present 
quality of papers, but if their employment does result in products 
whose qualities are somewhat different from our so-called standard 
papers it does not necessarily follow that such papers will not find 
a ready market. 

FACTORS JUSTIFYING AN INVESTIGATION OF HEMP HURDS. 

Hemp hurds form a crop waste, in that they necessarily are pro- 
duced in the raising and preparation of hemp fiber, and their present 
use and value are comparatively insignificant. 

The assembling of the hurds may be effected with economy, since 
the area in which hemp is handled with the use of machine brakes is 
restricted. Although it must be stated that the present annual 

1 For descriptions of investigations of some of these crops, see the list of publications at the end of this 
bulletin. 



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HEMP HUBDS AS PAPER-MAKING MATERIAL. 9 

supply would not be sufficient to justify the installation of a pulp mill 
nor would its transportation to existing mills appear feasible, it 
is expected that the available annual tonnage, especially in certain 
general sections, will increase, due to the increased use of the machine- 
brake. The present tonnage per annum is approximately as follows: 
In the region of Ohio and Indiana, 2,500 tons; in the Wisconsin sec- 
tion, 1,000 tons; in the California region, 1,400 tons. 

In years of adverse weather conditions there are often large areas 
of hemp which are not harvested on account of its poor quality; 
there are also large areas of cut hemp which become overretted, due 
to inclement weather. It has been suggested by some of the hemp 
raisers that this large amount of material might be utilized as a paper 
stock. In these cases the cost of the whole material would probably 
be somewhat higher than that of the hurds, because either all or part 
of the cost of harvesting and the total cost of breaking would have to 
be borne by the paper maker. Moreover, the quality of this material 
would be so very irregular and the supply so uncertain that it prob- 
ably would not appeal to the paper manufacturer. 

Without doubt, hemp will continue to be one of the staple agri- 
cultural crops of the United States. The wholesale destruction of 
the supply by fire, as frequently happens in the case of wood, is pre- 
cluded by the very 'nature of the hemp-raising industry. Since 
only one year's growth can be harvested annually the supply is not 
endangered by the pernicious practice of overcropping, which has 
contributed so much to the present high and increasing cost of pulp 
wood. The permanency of the supply of hemp hurds thus seems 
assured. 

The favorable location geographically of the hemp regions in re- 
lation to the pulp and paper industry is a factor of considerable 
importance. The Kentucky region is not at present in a position 
to supply hurds, as machine methods have not been adopted there 
to any appreciable degree. The Ohio and Indiana region, which at 
present has the greatest annual tonnage, with the prospect of an in- 
crease, is situated south of the Wisconsin and Michigan wood-pulp 
producing region and at a distance from the eastern wood-pulp 
producing regions; therefore, it is in a favorable position to compete 
in the large Ohio and Indiana markets. Since, as will be shown, 
the hurd pulp acts far more like soda poplar stock than sulphite 
stock, competition would be strongest from the eastern mills; in 
fact, the hurd stock might very possibly meet with favor as a book- 
stock furnish in the Michigan and Wisconsin paper mills, which are 
within the sulphite fiber-producing region. Because of its very close 
proximity to paper mills, this latter possibility applies with far 
greater force to the Wisconsin hemp region, where a considerable 
extension of the hemp industry is anticipated. 



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10 BULLETIN 404, U. S. DEPARTMENT OF AGRICULTURE. 



Fig. 3.— A representative sample of hemp nurds, natural size, showing hemp fiber and pieces of wood tissue. 

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HEMP HURDS AS PAPER-MAKING MATERIAL. 11 

CHARACTER OF THE MATERIAL. 

As received from Pierceton, Ind., the hurds consisted of a mixture of 
tangled hemp bast fibers and pieces of broken wood of the hemp 
stalk. (Fig. 3.) No reliable data were secured as to the propor- 
tion of bast fiber in the total shipment of 4 tons, although two 
hand separations of small representative samples gave results aver- 
aging 8 per cent. The chemical character of the material was such 
and the quantity was so small that any appreciable variation of the 
proportion should not affect materially the treating processes finally 
adopted, yet its presence in varying proportions undoubtedly would 



Fig. 4.— Fiber derived from the woody portion of the hurds. X 75. From a microphotograph. 

modify to some extent the quality of the resulting paper product. 
Since the length of the ultimate bast fiber averages about 22 mm. and 
the length of the ultimate hemp wood fiber averages 0.7 mm., it is 
natural to assume that the bast fiber would tend to increase the 
strength of paper produced from the hurds. (Fig. 4.) 

The broken pieces of wood contained in the hurds varied in length 
from mere particles which were somewhat finer than sawdust to pieces 
about 3 J inches long, exceptional pieces being found which measured 
6 inches in length. The majority of the long pieces were between 2 
and 3 inches in length. In thickness the pieces ranged from one-eighth 
of an inch, in case they were derived from the base of the hemp stalks, 
to about one sixty-fourth of an inch in those pieces which were 
derived from the top and branches of the stalks. In cross section the 



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12 BULLETIN 404, XT. S. DEPABTMENT OF AGRICULTUKE. 

pieces often were found to be a quarter or half of the rounded rectan- 
gular woody shell of the stalk, although there appeared to be no 
regularity in this respect. 

From the pulp-maker's standpoint the great irregularity in thick- 
ness, length, and mass of the woody pieces militates decidedly against 
economy in pulp production. The smaller pieces reduce by chemical 
treatment sooner than the larger fragments and are thereby over- 
treated, which results in a lower yield of cellulose fiber and a product 
composed of undertreated and overtreated fibers, the production and 
use of which are not satisfactory or economical. It probably would 
be f ound more satisfactory, therefore, to screen or sort the hurds and 
treat the various sizes separately and differently. 

Associated with the hurds was a small quantity of chaff and dirt, 
composed chiefly of sand, soil, particles of hemp leaves and flowers, 
and other extraneous matter. The sand and soil were present 
because of the practice of placing the stalks in shocks in the field, the 
butts of the stalks being in contact with the soil. It is a simple 
matter, however, to remove the chaff and dirt by sieving, and this 
practice was followed in most of the paper tests conducted with this 
material. 

CHARACTER OF THE TESTS. 

Because of the similarity of hemp hurds to other materials which^ 
have been tested by the Office of Paper-Plant Investigations, semi- 
commercial tests were conducted in cooperation with a paper manu- 
facturer without preliminary laboratory tests. Laboratory pulp and 
paper tests are regarded only as a preliminary to semicommercial 
tests and therefore are not employed unless the material in question 
presents new features which should receive investigation before 
larger sized tests are undertaken. 

The advantages of cooperative mill tests are many, among which 
may be mentioned the counsel and advice of the mill management 
and employees, the services of specialized and skilled labor, facilities 
for comparing the processes and the results of tests with commercial 
processes and results, and the use of commercial or semicom- 
mercial types and sizes of machinery. Tests conducted in this 
manner and on this scale are of a different quality than is pos- 
sible in those conducted in a laboratory, and the results are suscep- 
tible of commercial interpretation with a fair degree of reliability. 
It is found, in general, that the cost of securing such equipment and 
service for a complete and comprehensive test does not exceed $500, 
while the installation of an equally satisfactory equipment alone 
would cost at least $50,000 and in many cases very much more. 
Tests conducted in this manner constitute a direct demonstration to 
the manufacturer, and the results obtained are found to carry more 
weight when presented to other manufacturers for consideration. 



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HEMP HUBDS AS PAPER-MAKING MATERIAL. 13 

It is well known that the method of conducting tests necessarily 
varies with the size of the test. In the matter of yield determination, 
for example, laboratory tests may be on such a small scale that the 
weighing and sampling of the resulting cellulose fibers may be con- 
ducted by means of chemical laboratory apparatus and analytical 
balance, while in tests involving a matter of 5 to 10 pounds of material 
larger and different types of equipment are necessary. When 
the tests are so increased in size as to employ 300 or 400 pounds, 
still other types of equipment are necessary for the treatment of • 
the material and for a determination of the yield of fiber. In 
tests involving tons of material the equipment involves the use of 
machines. Accuracy in degree of control and in results will vary 
materially with the size of the test. As the size of the test increases, 
certain factors will vary in a beneficial manner, while others will vary 
in a detrimental manner, so it is a question for each investigator to 
decide, after taking all factors into consideration, as to the size of 
test which will give the most satisfactory results. In work of this 
nature it is found, on the whole, that better results are obtained in 
large tests, although the control of the factors and the determination 
of the yield of fiber are more difficult than in smaller tests. 

In the tests described in this bulletin, the Department of Agricul- 
ture employed a rotary digester of its own design, 1 comprising a shell 
.5 feet 5 indies in length by 4 feet in diameter, capable of holding 
about 300 pounds of air-dry hurds. It is believed that a test of this 
size is large enough to give satisfactory results and that the results 
are susceptible of commercial interpretation, while at the same time 
they are sufficiently small for complete control and to afford fiber- 
yield figures which are both accurate and reliable. Two such rotary 
charges gave enough fiber for one complete paper-making test. 

OPERATIONS INVOLVED IN A TEST. 

A complete test on hurds comprises seven distinct operations, and 
the method will be described, operation by operation, in the order 
in which they were conducted. 

Sieving. — The hurds for the first test were not sieved to remove 
eand and dirt, but the resulting paper was so dirty that sieving was 
practiced in all subsequent tests. The hurds were raked along a 
horizontal galvanized-iron screen, 15 feet long and 3 feet wide, with 
11} meshes per linear inch, the screen being agitated by hand from 
below. Various amounts of dirt and chaff could be removed, depend- 
ing on the degree of action, but it was found that if much more than 
3 per cent of the material was removed it consisted chiefly of fine 
pieces of wood with practically no additional sand or dirt; in most of 
the tests, therefore, the material was screened so as to remove 

1 *or t description of this rotary digester, see Brand, C. J., and Merrill, J. L., Zaoaton as a paper- 
nuking material, U. S. Dept. Agr. Bui. 309, p. 28, 1915. 



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14 BULLETIN 404, U. S. DEPARTMENT OF AGRICULTURE. 

approximately 3 per cent. It became apparent that a finer screen 
would probably serve as well and effect a saving of small but good 
hurds. 

Cooking: — Cooking is the technical term for the operation by which 
fibrous raw materials are reduced to a residue of cellulose pulp by 
means of chemical treatment. In these tests about *300 pounds of 
hurds were charged into the rotary with the addition of, a caustic* 
soda solution, such as is regularly employed in pulp mills and which 
tested an average of 109.5 grams of caustic soda per liter, or 0.916 
pound per gallon, and averaged 85 per cent causticity. Sufficient 
caustic solution was added to furnish 25 or 30 per cent of actual 
caustic soda, calculated on the bone-dry weight of hurds in the charge. 
After closing the rotary head, it was started rotating at the rate of 
one-half revolution per minute, and in about five minutes steam at 
120 pounds per square inch was admitted at such a rate that the charge 
was heated in one hour to 170° C, which is the theoretical equivalent 
of 100 pounds of steam pressure per square inch. It was found, 
however, that when the temperature reached 170° C. the pressure 
was usually 115 or 120 pounds instead of 100 pounds, due to air and 
gases inclosed in the rotary. At this point the rotary was stopped 
and steam and air relieved until the pressure dropped to 100 pounds, 
or a solid steam pressure. The temperature was maintained at this 
point for the number of hours required to reduce the hurds, which 
was found to be about five, after which the rotary was stopped 
and steam relieved until the pressure was reduced to zero, when the 
head was removed and the stock was emptied into a tank under- 
neath, measuring 5£ by 6 by 2 feet deep, where it was drained and 
washed. Samples of waste soda solution or "black liquor," which 
were taken from some of the "cooks" for analysis, were drawn while 
the stock was being thus emptied into the drainer. 

Determination of yield. — For determining the yield of cellulose fiber 
the stock in the drain tank was washed with water until free from 
waste soda solution, when, by means of a vacuum pump communi- 
cating with the space between the bottom and the false perforated 
bottom, the water was sucked from the stock, leaving the fiber with 
a very uniform moisture content throughout its entire mass and in a 
condition suitable for removing, sampling, and weighing for a yield 
determination. Tests have shown that it is possible to sample and 
calculate the yield of bone-dry fiber within 0.05 per cent of the actual 
amount. 

It has been found that stocks from different materials vary greatly 
in their ability to mat in the drain tank, thereby enabling a good 
vacuum to be obtained, some stocks permitting a 25-inch vacuum to 
be obtained, while others will not permit more than 5 inches. *<For 
this reason the moisture content of the stock will vary from 65 to 85 
percent. 



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HEMP HUBDS AS PAPBB-MAKING MATEKIAL. 15 

Washing and bleaching. — Washing and bleaching were performed 
for the purpose of bleaching the brown-colored cooked stock to a 
white product, since it was regarded as highly probable that the fiber 
would be suitable for book-paper manufacture. The colored stock 
was charged into a 400-pound beating and washing engine of regular 
construction and washed about one hour, the cylinder washer being 
covered with 60-mesh wire cloth in order to remove fine loose dirt 
and chemical residues. The washer was then raised, the stock 
heated by steam to about 40° C, and a solution of commercial 
bleaching powder was added in the quantity judged to be necessary, 
after which the stock was pumped to a large wooden tank, to remain 
and bleach over night. If the stock was bleached sufficiently white 
it was drained and washed from bleach residues, and if not more 
bleach was added until a good color was obtained. The bleaching 
powder used was estimated to contain 35 per cent of available 
chlorin, as this is the commercial practice, and the amount required 
was calculated to the bone-dry weight of the unbleached stock. 
More bleach is required for undercooked stock than for stock which 
is properly cooked or overcooked; therefore, the percentage of 
bleach required is an indication of the quality of the cooked stock. 
Since bleaching is usually more expensive than cooking, it is desirable 
to cook to such a degree that the consumption of bleach will be held 
within certain limits, depending on the raw materials used and the 
quality of paper to be produced. In these tests it was desirable so to 
cook the hurds that the consumption of bleach would not be over 
about 10 per cent of the fiber. 

Furnishing. — Furnishing is the operation of charging the beating 
engine with the desired kind or kinds of fiber in the proper proportion 
and amount and the adding of such loading and sizing agents as may 
be necessary. As shown in the record of results, the furnish in these 
tests consisted of hurd stock alone and of various proportions of 
hurds, sulphite fiber, and soda fiber. The percentages to be given in 
the record of the furnishes refer to the percentage of the total fiber 
furnish, and this likewise applies to the loading and sizing agents. 
In case sulphite or soda fiber was used, the commercial product in 
the dry state was charged into the beating engine and disintegrated, 
after which the hurd stock was added in the wet condition. 

Beating. — Beating is that operation concerning which the paper 
makers often say "there is where the paper is really made," and 
although the statement may not be literally true it contains a great 
deal of truth. It is the operation whereby the fibers are separated 
from each other, reduced to the proper lengths, and put in such a 
physical or chemical condition that they felt properly and form into a 
satisfactory sheet. It is probable that the quality of the sheet 
depends more upon the proper beater action than upon any other 
single operation. The action consists in drawing a water suspension 
of the fiber between two sets of rather blunt knives, one set being 



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16 



BULLETIN 404, U. S. DEPARTMENT OF AGRICULTURE. 



located in the bottom of a circulating trough and the other set on the 
periphery of a roll revolving just above the former set of knives. It 
is during this operation that the loading and sizing agents are incor- 
porated and the whole furnish is tinted either to produce a satisfac- 
tory white or the desired color. 

The term "paper making/' as used in this publication, means the 
operation of forming the finished sheet of paper from stock which has 
been furnished and prepared in the beater. In these tests a 30-inch 
Fourdrinier machine of regular construction was used, a machine 
which often is used for the production of paper for filling regular com- 
mercial orders. The machine is designed to cause the water suspen- 
sion of fibers to flow on to a traveling wire cloth, whereby the water 
drains away. More water is removed by passing the wet sheet through 
a series of press rolls, after which the sheet is dried on steam-heated 
drums and passed through polished iron rolls, which impart a finish 
to the sheet. A Jordan refining machine was employed in conjunction 
with the machine to improve further the quality of the fiber, and a 
pulp screen was used in order to remove coarse and extraneous mate- 
rials from the fiber. 

DESCRIPTION OF TESTS. 

The nature of each complete paper test and the dependence of 
each operation on the others were such that it does not seem advisable 
to submit the results of the seven tests in tabular form. The numer- 
ous cooks, however, which furnished the pulp for the paper tests are 
presented in Table I in all essential detail. 

Table I. — Data on cooking hemp hurds. 



Cook No. 



Caustic 

soda used 

(percentage 

of bone-dry 

hurds), 



Strength of 

caustic soda 

(grams per 

liter). 



Causticity 
of soda 
solution. 



Time 
(hours). 



Cooking. 



Tempera- 
ture(°C.) 



Yield of 

bone-dry 

fiber (per- 

centageof 

bone-dry 

unsieved 

hurds). 



294. 
205 
296. 
901. 
802. 
303 
804 
306. 
306. 
307. 
308. 
309. 
310 
311. 
312 
313 
314 
315 
316. 
317 
318 
819 
320 



20.6 

21 

21.6 

20.3 

21.9 

24.4 

24.2 

25 

25 

27.8 

26.7 

26 

27.3 

27.1 

27.2 

28.3 

29.1 

29.1 

29.4 

30 

29.6 

29.6 

29.4 

29.3 



100 

100 

100 

100 

100 

100 

100 

100 

100 

107.5 

107 

107 

107 

107 

107 

116.5 

113.1 

109 

109 

109.5 

109.5 

107 

107.5 

107.6 



75.3 
75.3 
75.3 
75.3 
82.6 
82.6 
84.3 
84.3 
84.3 
84.3 
84.4 
84.4 
84.4 
84.4 
84.4 
85.5 
84.9 
83.9 
83.9 
84.9 
84.9 
84.8 
84.2 
84.2 



166 
166 
166 
166 
166 
166 
166 
170 
170 
166 
170 
170 
170 
170 
170 
170 
170 
170 
170 
170 
170 
170 
170 
170 



0) 



44.1 

39.5 
39.4 
36.5 
38.1 

37.3 

87.0 
86.8 
85.9 

35.2 

34.9 
87.2 
87.0 
87.7 
35.4 



» Stock not used; dirty. 



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HEMP HXJRDS AS PAPEB-MAKING MATERIAL. 17 

Discussion of the various cooks will be given in connection with 
the descriptions of those paper tests in which the stocks from the cooks 
were used, since a stock and its cooking condition can be judged ade- 
quately only after it has been put through the various processes and 
into the finished sheet of paper. 

The first test consisted in making four separate cooks, Nos. 293, 294, 
295, and 296, of approximately 300 pounds each, dividing the total 
stock into two parts and making two separate paper tests. The 
first test was made primarily in order to learn some of the qualities 
and characteristics of the stock and to get the machinery equipment 
adjusted properly. The yield of fiber was not determined in this 
preliminary test, since the knowledge of it was not essential at this 
stage of the work. The cooked stock which was emptied into the 
drainer to be washed free from black liquor was composed largely of 
whole pieces of hurds, but only slight pressure between the fingers 
was required to crush the pieces. In the case of wood, this condition 
ordinarily would indicate undercooking, but might not in the case of 
hurds. Further observation on the action of the cooked stock during 
subsequent processes was necessary in order to judge of its quality or 
the suitability of the cooking conditions. The total cooked stock, 
about 600 pounds, was divided into two portions of 200 and 300 
pounds, respectively, and work was continued on them separately. 
The 200-pound test, designated as run No. 135, was put into a 350- 
pound washing engine, washed one hour, and given a total light brush 
of 2\ hours. The washing removed a great amount of dirt, but the 
engine did not reduce the hard stock as much as was desired. After 
heating the stock in the beater to 40° C, it was bleached with bleach- 
ing-powder solution, 94 gallons at 0.418 pound* bleach per gallon, 
equivalent to 19.7 per cent of the fiber. This percentage of bleach is 
regarded as too high for stock intended for book-paper manufacture, 
and subsequent cooks therefore were given harder treatment in order 
to reduce this figure. After draining and washing free from bleach 
residues, the stock was furnished in the beater with 13 per cent of 
clay, 1 per cent of resin size, and 2.5 per cent of alum, was tinted 
blue, given one hour's light brush, and pumped to the stock chest. 
When running it on the paper machine, the Jordan refiner seemed 
to have little effect in reducing shives of undertreated wood, which 
indicated further the necessity of harder cooking. The furnish acted 
well on the paper machine at 70 feet per minute, but appeared some- 
what too "free" on the wire. The paper produced from this test is of 
very low quality, due to the improper preparation of the stock, lack 
of sufficient bleach, the use of too small an amount of blue tinting, and 
the presence of an excessive amount of dirt, sand, and shives. The 
excessive amount of dirt and sand suggested the sieving of the hurds 
before cooking, and this was performed in all subsequent cooks. 



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18 BULLETIN 404, U. S. DEPARTMENT OF AGRICULTURE. 

The finish of the sheet is very poor, due to the fact that the calender 
stack was composed of very light rolls which did not have a satisfac- 
tory surface, yet the stack is known to be able to produce better finishes 
if the proper stock is employed. 

Rim No. 136 was made on the 300-pound portion of stock from 
cooks Nos. 293, 294, 295, and 296, and in essentially the same manner 
as run No. 135. The stock was washed one hour, but given a brush 
of three hours, and this brush was harder than in run No. 135. 
Bleach to the extent of 19.8 per cent of the fiber was used, assisted 
by 1 pint of oil of vitriol, and the resulting color was an improvement 
over that of run No. 135. After adding 13.5 per cent of clay and 
sizing with 1.1 per cent of resin size, the furnish was given one-half 
hour's light brush, tinted, and run on the machine, which was set 
at 70 feet per minute. This stock acted better on the wire and gave 
no trouble on the machine, but it still seemed to be impossible to 
reduce the wood shives by manipulation of the Jordan refiner. The 
resulting sheet is an improvement over that produced by No. 135, 
but is far from satisfactory. 

Run No. 138 was made from hurds which, as in all subsequent teste, 
were sieved on a llj-mesh wire screen until practically all the loose 
dirt and sand was removed, which operation caused a loss averaging 
3 per cent of the hurds. Stock from cooks Nos. 302 and 303 was 
used for this run and the increased amount of caustic soda and the 
increase in the time of cooking gave a stock of better appearance than 
those of preceding tests. 

The stock, amounting to 231 pounds dry weight, was washed and 
at the same time given a light brush for one hour only, after which 
it was bleached wilh 17 per cent of bleach without the addition of 
acid. Since the preceding paper appeared somewhat weak and had 
a low tearing quality, it was decided to use a furnish of 15.7 per cent 
bleached sulphite and 84.3 per cent bleached hemp-hurd stock. 
After loading with 13.1 per cent of clay and sizing with 1.1 per cent 
of resin size, the furnish was given a medium brush for one hour, 
tinted, and run on to the machine at 70 feet per minute. The stock 
gave no trouble on the machine, but it was impossible to judge the 
effect of the Jordan refiner, because through an oversight the machine 
chest had not been oleaned since previous use on an unbleached 
yucca material. It is believed, however, that sheet No. 138 shows 
improvement in the preparation of the hurd pulp. 

Rim No. 139 was made from stock of cooks Nos. 304 and 305, 
in which still more caustic soda was employed and the time and tern* 
perature of cooking were increased, giving a yield of total fiber of 
40.7 per cent of the sieved or 39.4 per cent of the unsieved hurds. 
The cooked stock still seemed to be undertreated, but it must be 
remembered that in working with any new raw material it is impos- 



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HEMP HXJBDS AS PAPEB-MAKING MATERIAL. 19 

able to know in advance how the properly treated material should 
appear. A washing of one hour was given while the roll was lowered 
from a light to a medium brush, after which the stock was bleached 
with 17.1 per cent of bleach without the aid of acid. Since sulphite 
stock improved the previous paper, this bleached stock was used 
in a furnish of 16.6 per cent sulphite and 83.4 per cent hurds, loaded 
with 16.7 per cent clay, sized with 1.4 per cent resin size, given a 
medium brush of two hours, tinted, and run on to the machine at 
70 feet per minute. The Jordan refiner seemed to have little effect 
in reducing shives and was therefore left " just off." No trouble was 
experienced with the stock on the machine, and the sheet is an 
improvement over previous samples. 

Run No. 140 was made from cooks Nos. 306 and 307, in which 
more caustic soda was employed than in any previous cooks and at a 
higher concentration, the fiber yields of which averaged 37.3 per cent 
of the unsieved hurds. Not much improvement was apparent in 
the cooked stock, in spite of the increased severity of cooking. The 
stock was washed and given a medium brush for one hour, bleached 
with 11.9 per cent of bleach, assisted with one-half pint of oil of 
vitriol, and mado into a furnish of 14.9 per cent sulphite and 85.1 
per cent of the hurd stock. After loading with 14.7 per cent of clay 
and sizing with 1.28 per cent of resin size, the furnish was given two 
hours' medium brush, tinted, and run on to the paper machine at 
70 feet per minute. Again the Jordan refiner did not seem to reduce 
the wood shives sufficiently, and it was left "just off." No trouble 
which could be attributed to the stock was experienced on the paper 
machine. The color of the resulting paper is due to the use of too 
little blue in tinting and probably in some measure to the use of too 
low a percentage of bleach. 

Run No. 141 was made from the stock of cooks Nos. 308 and 309 
in practically the same manner as run No. 140. The stock was 
washed and brushed one hour, bleached (the record of the amount 
of bleach was lost), made into a furnish of 14.7 per cent of sulphite 
and 85.3 per cent of hurd stock, loaded with 14.9 per cent of clay, 
sized with 1.26 per cent of resin size, given one hour at a medium 
brush, tinted, and run on to the machine. The Jordan refiner was 
able to reduce the wood shives to a somewhat greater degree than in 
previous runs and was held at a medium brush. The stock acted 
well on the machine and produced a sheet of better quality than any 
preceding, with the exception of the color, which was due to using too 
small a quantity of blue. 

Among the cooks made for run No. 142 are Nos. 312 and 313, in 
which the concentration of the caustic soda was raised to 113 and 
116 grams per liter and the percentage employed was also increased. 
In spite of these increases the stock from these two cooks did not 



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20 BULLETIN 404, U. S. DEPARTMENT OF AGRICULTURE. 

show any appreciable improvement when dumped from the rotary. 
Stock from cooks Nos. 310, 311, and 312 was given a medium brush 
and washing of one hour, bleached with 10.95 per cent of bleach, 
made into a furnish- consisting of 15.2 per cent of sulphite and 84.8 
per cent of hurd stock, loaded with 15.2 per cent of clay, sized with 
1.28 per cent of resin size, given a medium brush for one hour, tinted, 
and pumped to the stock chest. Stock from cooks Nos. 313 and 314 
was treated in exactly the same manner, except that 11.4 per cent 
of bleach was used. It was pumped to the stock chest and mixed 
with the furnished stock from cooks Nos. 310, 311, and 312. A 
medium Jordan brush was given the stock and it acted well on the 
paper machine, which was speeded to 75 feet per minute. There 
seems to be a tendency in the hurd stock to crush a little at the 
" dandy roll," and although the marks are not removed by the calen- 
der stack which was employed in those tests it was found that one 
"nip" on the supercalenders renders them practically imperceptible 
and it is believed that the proper size and weight of calender stack 
would entirely remove these marks. All of the papers produced 
up to this point are somewhat lacking in the bulk desired in a book 
paper; therefore, in the two following runs soda-poplar stock was 
included in the furnishes. 

In run No. 143 stock from cooks Nos. 315 and 316 was given a 
medium brush and washing for one hour and was medium brushed 
for one hour more, bleached with 11.3 per cent of bleach assisted 
with one-half pint of oil of vitriol, made into a furnish of 16.5 per 
cent of sulphite, 22.3 per cent of soda poplar, and 61.2 per cent of 
hurd stock, loaded with 22 per cent of clay, sized with 1.38 per cent 
of resin size, given a hard brush for one hour, tinted very strongly, 
and pumped to the stock chest. This stock was beaten to a greater 
extent than in previous runs. The stock was run on the paper 
machine at a speed of 75 feet per minute, using a medium Jordan 
brush, and no trouble whatsoever was experienced. Not over 2 
pounds of "broke" was produced during the whole run, and that 
was in the "threading" of the machine. The color of the sheet is 
entirely satisfactory for many uses. The wood shives apparently 
were reduced to a satisfactory degree. Experienced paper makers 
commented very favorably oq. the running of this furnish and the 
quality of the paper produced. 

Run No. 144 was intended as a duplicate of run No. 143. Stock 
from cooks Nos. 317 and 318 was given a medium brush and washing 
for one hour and a further medium brush of one hour, bleached with 
11.4 per cent of bleach, and made into a furnish composed of 15.5 
per cent of sulphite, 23.5 per cent of soda poplar, and 61 per cent of 
hurd stock, loaded with 21.4 per cent of clay, sized with 1.17 per cent 
of resin size, hard brushed for one hour, tinted by th£ expert colorer 



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HEMP HTJBDS AS PAPER-MAKING MATERIAL. 21 

of the company, and pumped to the stock chest. Stock from cooks 
Nos. 319 and 320 was treated in exactly the same manner except 
that the stock was bleached with 12.1 per cent of bleach and pumped 
to the stock chest to mix with the former furnish. The stock acted 
very well on the machine, which was speeded to 75 feet per minute, 
with the Jordan refiner set at a medium brush. The sheet is as good, 
if not better, than that of run No. 143, and it is also a good illustra- 
tion of the extent to which proper tinting will enhance the general 
appearance of a paper. The poor appearance of the samples of 
previous runs is due largely to lack of proper tinting. Various 
degrees of whiteness, however, are demanded by the trade. 

COMPARISON OF THE TESTS AND COMMERCIAL PRACTICE. 

In work of this nature and on this scale it is practically impossible 
to arrive at a cost figure which would be susceptible of commercial 
interpretation, and in this preliminary publication nothing will be 
attempted beyond a comparison of the process used with the hurds 
with that process commercially applied to poplar wood. The process 
last used with the hurds should not be regarded as final, satisfactory, 
or most suitable, as it has been shown that progress was being made 
up to the conclusion of the work. 

In comparing the method of using hurds with the method of han- 
dling poplar wood, a difference is apparent on the delivery of raw 
material at the mill. Ordinarily, poplar is received at the mill in 
the form of logs about 4 feet in length, which may be stored in piles 
in the open. Hurds .very likely would be received baled, and it would 
seem advisable to store them under cover for the following reasons: 
(a) Baled hurds would probably absorb and retain more water 
during wet weather than logs of wood, thereby causing excessive 
dilution of the caustic liquor; (i) prolonged excessive dampness 
might create heating and deterioration unless the hemp were properly 
retted; (c) wet hurds could not be sieved free from sand and chaff. 
Should further work show that the first two reasons need not be 
taken into consideration, the third objection might be overcome by 
sieving the hurds before baling. Even then, it is probable that 
baled hurds stored in the open would accumulate and retain con- 
siderable dirt from factory chimneys, locomotives, and wind. 
Checked pulp wood exposed in the open invariably suffers from 
these causes. 

In the preparation of the raw material for the digesters there is 
likewise considerable difference between hurds and poplar wood. 
The former apparently requires only a moderate sieving to remove 
sand and chaff, which operation doubtless would require only a 
small amount of labor and the installation of some simple machinery 
of low power consumption. In preparing poplar for digestion, the 



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22 BULLETIN 404, U. S. DEPARTMENT OF AGEIOULTUBE. 

4-foot logs are chipped by a heavy, comparatively expensive chipper 
of high power consumption, after which the chips are sorted by 
sieving, the large pieces being rechipped. There would be a note- 
worthy difference in the installation, operating, and depreciation 
costs of the two equipments, and this difference would counterbal- 
ance to a considerable extent the difference in cost of raw material 
storage. 

It is possible that in the use of the chip loft more care would have 
to be exercised in using hurds because of the tendency of the bast 
fiber to cause lodgments, but this should not be considered a serious 
difficulty. 

The weight of hurds which are capable of being charged into a 
rotary is a decidedly unfavorable factor. The weight of a cubic 
foot of hurds varies somewhat with the proportion of bast fiber, 
but averages about 5.4 pounds, which, compared with a cubic foot 
of poplar chips at 8.93 pounds, represents a digester charge of 60.5 
per cent of the weight of a poplar-wood charge, or, in terms of fiber 
capacity, the hurds charge would yield 38.6 per cent as much fiber 
as the wood charge. The hurds upon being baled for transporta- 
tion may be broken and crushed to such a degree that the weight 
of the charge may be increased, and it might be found possible to 
increase the charge weight by steaming or by the employment of 
tamping devices. This small weight of charge constitutes one of the 
most serious objections to the use of hurds in paper manufacture. 

In those tests in which the most satisfactory results were obtained, 
the cooking conditions were 29.5 per cent of caustic soda at a concen- 
tration of 107 grams per liter and a causticity of 84.0 per cent acting 
at a temperature of 170° C. for five hours, or a total time of seven 
hours. The steam condensation in the rotary used for these tests 
was abnormally high, due to the fact that the steam supply pipe was 
uncovered for a considerable distance and the rotary was entirely 
uncovered. It is believed, therefore, that a larger amount of caustic 
was necessary than would otherwise have been the case. This 
belief is strengthened by the quality of the waste liquor from one of 
the later cooks, which gave on analysis 16.85 grams per liter of free 
caustic soda and showed a causticity of 27.75 per cent. These data 
show that only 67.3 per cent of the total caustic employed was actu- 
ally consumed in the cooking operation, which percentage is lower 
than obtains in practice. The stock from this cook was bleached 
with 11.5 per cent of bleach. But even as the figures stand, the 
comparison with poplar cooking practice is as follows: 29.5 per cent 
caustic soda used as against 22 to 25 per cent; 107 grams per liter 
as against 100 to 110; 84 per cent causticity is little different than 
obtains in practice; 170° C. is about commercial practice; five hours 
at pressure as against four to six hours; seven hours' total time as 



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HEMP HUBDS AS PAPEB-MAKING MATERIAL. 23 

against possibly six to eight hours; 11.5 per cent bleach as against 
8 to 10 per cent. Thus, it is evident that the cooking conditions 
employed were slightly more severe and expensive than those in 
commercial use with poplar wood. 

The yield of total fiber obtained from the hurds may be placed at 
35 per cent of bone-dry fiber calculated on the bone-dry weight of 
hurds used, or 33.1 per cent of air-dry fiber calculated on air-dry 
hurds. The yield of bleached fiber was not determined in this pre- 
liminary work, but may be safely estimated as 30 per cent, which i* 
low when compared with a yield of about 47 per cent of bone-dry 
bleached fiber from bone-dry poplar wood. It is believed quite 
possible that satisfactory cooking conditions may be found which will 
give a higher yield than was obtained during these tests. The stock 
should be classed as easy bleaching, and 11.4 per cent of bleach is a 
satisfactory figure, although a little high. 

As to beating cost, in the last two and most satisfactory tests the 
total washing and beating time was three hours, which may be about 
an hour more than ordinarily is used in making papers of this grade, 
although the practice varies to a considerable extent. 

In regard to furnish, there is such a diversity of practice that it is 
difficult to make a comparison, but if the hurd stock can be produced 
as cheaply as soda-poplar stock, the furnish used in these last two 
tests should be regarded as satisfactory to the book and printing 
paper manufacturer. 

The finish of the paper was not all that might be desired, but that 
was due almost entirely to the calender stack available for the work, 
which was composed of nine light rolls, many of which were about 
6 inches in diameter and which had not been reground for some time. 
From a small test on a large calender stack it was readily shown that 
the paper produced is capable of taking a satisfactory finish. 

This comparison, satisfactory in many respects, develops two 
factors which are decidedly unfavorable to hemp hurds, namely, raw- 
material storage and digester capacity, and they must be taken into 
full account in considering the paper-making value of this material, 
although it should be recognized that investigation may result in the 
material improvement of these conditions. Moreover, it is not at all 
improbable that further investigation would develop more satisfac- 
tory treating conditions and more suitable furnish compositions, and 
the belief in this possibility is strengthened by the fact that material 
progress was being made at the conclusion of this preliminary work. 

Calculations on the raw material and acreage for a permanent sup- 
ply for a pulp mill producing 25 tons of fiber a day for 300 days per 
annum, or 7,500 tons per annum, give the comparison between hurds 
and wood shown in Table II. 



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24 BULLETIN 404, XJ. S. DEPABTMENT OF AGBICTJLTXJBE. 

Table II. — Comparison between wood and hemp hurds. 





Pulp yield. 


Raw material 

required per 

year. 


Annual 
growth 
per acre. 


Acres required for sus- 
tained supply. 


Material. 


Far 25-ton 
null. 


Fori ton 
of fiber 
per year. 


Wood 


Two cords 

yield 1 ton of 

fiber. 
One ton yields 

600 pounds 

of fiber. 


15,000 cords.... 
25,000 tons.... 


0.37 cord 
(about 
0.55 ton). 

2.5 tons... 


40,500 
10,000 


5.4 


Jlemp nurds. . . . . , . . , 


1.33 







The most important point derived from this calculation is in regard 
to areas required for a sustained supply, which are in the ratio of 4 
to 1. Every tract of 10,000 acres which is devoted to hemp raising 
year by year is equivalent to a sustained pulp-producing capacity of 
40,500 acres of average pulp-wood lands. In other words, in order to 
secure additional raw material for the production of 25 tons of fiber 
per day there exists the possibility of utilizing the agricultural waste 
already produced on 10,000 acres of hemp lands instead of securing, 
holding, reforesting, and protecting 40,500 acres of pulp-wood land. 

The annual growth per acre, although decidedly in favor of hurds, 
has little bearing on the project, because the utilization of the hurds 
is subordinate to the raising of hemp, and the paper manufacturer 
probably could afford to use only hurds resulting from the hemp 
industry. 

PHYSICAL TESTS OF THE PAPERS PRODUCED. 

Samples of paper produced in the seven tests were submitted to 
the Leather and Paper Laboratory of the Bureau of Chemistry. The 
report of that bureau on its tests is given in Table III. 

Table III. — Report of the Leather and Paper Laboratory of the Bureau of Chemistry on 
papers manufactured from hemp hurds. 



Labora- 


Run 
No. 


Ash. 


Weight of 500 
sheets. 


Thick- 
ness, 

lApooo. 


Strength (Mullen). 


Strength 
factor (25 


Folding endur- 
ance. 


tory No. 


25 by 38. 


25 by 40. 


Aver- 
age. 


Maxi- 
mum. 


Mini- 
mum. 


"8* 


Longi- 
tudinal. 


Trans- 
verse. 


31570 

31571 

31572 

31573 

31574 

31575 

31576 


144 
143 
142 
141 
140 
139 
138 


Perct. 
13.9 
14.5 
9.5 
10.9 
11.4 
13.4 
10.4 


Pounds. 
48 
49 
49| 
48 
42 
55 
50 


Pounds. 
52 

S* 

58 
59 


33 
35 
33 
38 
30 
40 
40 


15.0 
14.0 
19.0 
16.5 
14.5 
19.5 
20.0 


17.0 
14.0 
20.0 
18.0 
16.0 
20.0 
20.0 


11.0 
13.0 
19.0 
11.0 
13.0 
17.0 
19.0 


a 30 

.28 
.37 
.33 
.33 
.34 
.34 


5 
4 

8 
10 
7 
8 
23 


8 
4 
6 
8 
6 
6 
15 



There is no system of numerically recording the general appearance 
and "look through' ' of a paper, but it can be stated that only papers 



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HEMP HUEDS AS PAPEB-MAKING MATERIAL. 25 

Nos. 143 and 144 are satisfactory in these respects, the other sam- 
ples being more or less thickly specked with shives. The general 
character and tests of these papers correspond very closely with 
No. 1 machine-finish printing paper, according to the specifications 
of the United States Government Printing Office, which call for a 
sheet not exceeding 0.0035 inch in thickness, strength not less than 
12 points, free from unbleached or ground wood pulp, and ash not 
over 10 per cent. The strength factor of such papers is about 0.28. 
The ash should not be over 10 per cent for this grade of paper, but 
in spite of the larger amount used the physical tests are sufficiently 
high. It is to be noted that the physical tests of samples Nos. 138 
to 142, inclusive, are higher than in Nos. 143 and 144, in which 23 
per cent of soda poplar was used, which shows clearly that hemp- 
hurd stock imparts strength and folding endurance to a greater 
extent than does soda-poplar stock. From these preliminary tests it 
would be concluded, therefore, that hemp-hurd stock acts similarly 
to soda-poplar stock, but will produce a somewhat harsher and 
stronger sheet and one of higher folding endurance. Undoubtedly, 
there is more dirt in the samples than would be tolerated by the 
trade, but this was to be expected, since in this preliminary work the 
raw material was sieved by hand screens instead of by automatic 
machines which would sieve more thoroughly. 

CONCLUSIONS. 

There appears to be little doubt that under the present system of 
forest use and consumption the present supply can not withstand 
the demands placed upon it. By the time improved methods of 
forestry have established an equilibrium between production and 
consumption, the price of pulp wood may be such that a knowledge 
of other available raw materials may be imperative. 

Semicommercial paper-making tests were conducted, therefore, on 
hemp hurds, in cooperation with a paper manufacturer. After 
several trials, under conditions of treatment and manufacture which 
are regarded as favorable in comparison with those used with pulp 
wood, paper was produced which received very favorable comment 
both from investigators and from the trade and which according to 
official tests would be classed as a No. 1 machine-finish printing 
paper. 



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PUBLICATIONS OF UNITED STATES DEPARTMENT OF AGRICULTURE 
RELATING TO MATERIALS FOR PAPER MAKING. 

AVAILABLE FOB FREE DISTRIBUTION BT THE DEPARTMENT. 

Suitability of Longleaf Pine for Paper Pulp. Department Bulletin 72. 

Zacaton as a Paper-Making Material. Department Bulletin 309. 

Utilization of American Flax Straw in the Paper and Fiber-Board Industry. Depart- 
ment Bulletin 322. 

Crop Plants for Paper Making. Bureau of Plant Industry Circular 82. 

Pulp and Paper and Other Products from Waste Resinous Woods. Bureau of Chemistry 
Bulletin 159. 

Paper-Making Materials and Their Conservation. Bureau of Chemistry Circular 41. 

Paper Birch in the Northeast. Forest Service Circular 163. 

Experiments with Jack Pine and Hemlock for Mechanical Pulp. Forest Service. 

Forest Products Laboratory Series, unnumbered bulletin. 1912. 

FOB SALE BT THE SUPERINTENDENT OF DOCUMENTS, GOVERNMENT PRINTING 
OFFICE, WASHINGTON. D. C. 

The Grinding of Spruce for Mechanical Pulp. Forest Service Bulletin 127. Price, 

15 cents. 
Progress in Saving Forest Waste. Yearbook, 1910. Price, $1. 
The Utilization of Crop Plants in Paper Making. Yearbook, 1910. Price, $1. 
26 



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